(1) Field of the Invention
This invention relates to a gravity structure.
More particularly, the invention relates to a gravity structure such as a caisson, concrete block and L-shaped block that are used for the construction work of breakwaters, river and sea walls and wharfs.
(2) Description of the Prior Art
It is necessary that these gravity structures are fixed at the points to be installed and they do not move. It is, however, difficult to install these gravity structures fixedly to foundation surfaces and they are liable to be moved by external forces. When breakwaters are constructed by using caissons, the seabed is excavated and levelled, and rubble is laid on the levelled surface to form a foundation mound. The caissons are then sunk onto this foundation mound and they are filled with rubble, gravel, sand and concrete, thereby constructing breakwaters. In another method of construction work, asphalt mats are laid over a foundation mound, caissons are sunk onto the asphalt mats and rubble is laid in the spaces among the caissons to a certain height in order to prevent the caissons from moving, and further, the caissons are filled with stone, sand and concrete.
The breakwaters thus constructed naturally receives wave pressure from the open sea. The resistance of caissons against the wave pressure from the open sea depends upon the caissons' own weights, the friction between the bottoms of caissons and the foundation mound, and the amount of rubble that is laid on the sides of caissons.
Since the breakwaters using caissons are constructed simply by placing the caissons on the foundation mound as described above, there has been a problem that the caissons are liable to move when they receive any external force such as wave pressure.